Oscilloscope



March 31, 1953 R. C. HERGENROTHER ETAL March 31, 1953 R. c. HERGENROTHERT AL OSCILLOSCOPE 3 Sheets-Sheet. 5'

Filed July 19, 1952 a 5: M T

W 5. a m H a f m M e51 flew TTOR/VEY Patented Mar. 31, 1953 UNITEDSTATES PATENT OFFICE USCILLOSCOPE Rudolf G. Hergenrot'her, West Newton,and Hermann Gun-the: Rudenberg, Newton, Mass., as; signers to RaytheonManufacturing Company, Newton, Mass a corporation of DelawareApplication July 19, 1952, Serial No. 299,846

11 Claims. 1

This invention relates to a cathode ray tube oscilloscope adapted to;measure highv voltage signals, and, more particularly, relates to anelectrostatic deflection system a reduced deflection sensitivity for usein an oscilloscope capable of measuring high voltage signals.

An object of this invention is to provide an electrostatic deflectionsystem having a reduced deflection sensitivityi Another obiect ofinvention is to provide-animproved. oscilloscope for the measurement ofhigh voltage signals.

Still another object of this invention is to provide an oscilloscopehaving' a deflection system of reduced deflection sensitivity "capableof being operated directly at high voltages.

A further object of this invention is to pro,- vide an oscilloscope wliich may be calibrated with an accelerating voltage which is smallcompared with the voltage to be measured H A final object of thisinvention is to provide an oscilloscope for of signals of a singlepolarity which. substa -tially the entire portion of the oscilloscopescreen for presentatlon.

As radar transmitterpowers have increased, requiring higher peal; pulsevoltages and narrower pulse widths, the problem of measuring modulatorpulse shapes and amplitudes has become increasingly difllcult.

The conventional method of measuring high voltages by using a voltagedividing network to reduce the voltage to a level which can be appliedto the deflection plates of a cathode ray oscilloscope runs into seriouslimitations when voltages of the order '01 106 km and puls widths of the'order'of a fraction of a microsecond are to be measured. Thesedifficulties arise because the required resistor power dissipation ishigh and the resistor distributed capacity .hls'h. Direct measurement ofthe Deal: pulse voltage by rectification is also restricted becausediodeslsuits able for operation "at such high voltages are notavailable.

The measurement of the shape and amplitude of narrow high voltageswould, however, be-

come simple and accurate if :a cathode ray tube,

high-voltage levels, were available. Since the Y 2 deflection factorofvolts per radian beam deflection of an eletcrostatic deflection systemis proportional to the anode voltage, it would be possible in such atube to calibrate the electron spot deflection using a low anode voltageand to measure voltages a high anode voltage, thus considerably reducingthe D. C. calibration voltage requirement by a factor of 5 or '10.

The deflection electrodes must be designed so that high potentialgradients, which might cause cold emission, are avoided. Also asubstantial insulation surface length must separate the el'ec trodes in'the vacuum envelope as well as outside, to avoid insulation breakdown.The dcflection factor of volts per radian of electron beam deflection ofthis electrostatic deflection system is required to be about fifty timesthat of a conventional oscilloscope tube and this factor is required tobe essentially constant over the deflection range.

If is the voltage between deflection plates and c is the capacitance perunit width of the deflection plates; it has been shown by H. 'G'.Rudenberg in an article appearing at pages 279 through 284 in theJournal of Applied Physics, vol. '16, No. 5, May 1945, entitledDeflection Sensitivity of Parallel wire Lines in Cathode Rayoscillographs that the change of angle 0 of the beam in radians producedwhile travelingthrough' the deflection field is given by where is theaccelerating potential which is the mean direct current potential of thetwo deflection plates with respect to the cathode of the electron gunand. usually the same as the second anode potential and so is thedielectric constant of free space.

From Equation 1 it is apparent that, in order to increase the deflectionfactor of Volts per radian beam deflection the plate-to-p'latecapacitance of the deflection system should be made as low as possible.This can lee-accomplished byma'king the plates shorter and increasingtheir separation. If the length of the plates is decreased sufficientlyand the 3 spacing is increased sufficiently, the plates shrink to twoparallel wires whose separation is large compared with their diameters.

Since the capacitance per unit length of a parallel-wire line is givenby where r is the radius of the wires and d, the center-to-centerseparation of the wires, the beam deflection angle 0, as given byEquation 1,

becomes g .i 3 2V coshg The deflection factor is therefore given by Vcosh- If it is desired to obtain a deflection oflone radian with ameasured deflection voltage of 100 kv. while using an anode voltage ofsay 10 kv.. Equation 4 gives The lower limit'of r is set by coldemission effects which require that the potential gradients at theconductor surfaces should be less than 10 volts per centimeter. From theabove computation it is evident that 'itis practically impossible tomeet the deflection requirements for such high voltages by modificationof the conventional deflection system in the forrnofa parallel-wire lineand that someother type o'f deflection system must be devised. 1 Onemethod of attenuating an electric field is to set up the field between afirst electrode and a second electrode which is surrounded by anapertured shield.

In accordance with this invention, the high voltage deflection electrodeof the oscilloscope is partially shielded so thatonly the field fringingthrough an aperturein. the shield can deflect the electron beam. Byproperly dimensioning the aperture any reasonable reduction ofdeflection sensitivity (increase in deflection factor) may be obtained,since only a comparatively few electric lines of force reach-through theaperture and act on the electron beam'rather than terminating on theshield.

For example, one form of electrostatic deflection assembly maycompriseiacylindrical high voltage deflection electrode surrounded by acoaxial cylindrical shield containing a small slot or aperture therein.The aperture is arranged in juxtaposition with the other deflectionelectrode of the cathode ray tube which may be at ground potential. Byproper adjustment of the aperture in the shield, a comparatively largedeflection factor and a deflection factor which is substantiallyindependent of deflection angle may be obtained.

Many voltages to be measured, such as the output pulses of radarmodulators, are negative with respect to ground. The shielded electrodeof the deflection assembly is used as the high voltage electrode and theother electrode, together with the accelerating anode and shield, isconnected to ground. The deflection field will, therefore, cause theelectron beam to be bent away from the shielded electrode. If thedeflection system were aligned with the cathoderay tube axis, onlyone-half the fiuorescen' screen would be available for displaying thepulses. ""Irlorderto utilize the entire face of the fluorescent screenfor pulse display, the deflection system is displaced from the cathoderay tube axis and a fixed deflection is imparted to theelectron beam byeither an electrostatic field Off by an electromagnetic fieldsurrounding the cathode ray tube, causing the beam to pass through thedeflection field to one edge of the fluorescent screen.

The deflection factor of the tube is calibrated by using a readilyobtainable measured anode voltage which may, for-example, be of theorder of magnitude of one or two kv. and applying ameasureddirectcurrentvoltage to the deflection systemsufflcient toproduce full scale deflection. Calibration of' the cathode ray tubeis'based on the fact that-the deflection factor is-directly proportionalto the anode voltage V; that is, the deflection factor during actualpulse measurement is equal to the-calibration deflection factormultiplied by the ratio of the anode voltage used during measurement andthe anode voltage used during calibration.

Suppose that the screen is to be calibrated for 'a. full scaledeflectionEm volts in the neighborhood of by. and an anode voltage Vm isneeded-to produce said deflection. It is impractical to apply ameasured'direct current voltage 7 Elm of this magnitude to the cathoderay tube for calibration purposes since direct current voltages of suchlarge magnitude are costly and difllcult togenerate'f and control. Ifthe anode is-operated-j at avalue Vc which is times that; O f Vm where tis any number, then a defle tion. v ltag 0 of. only.

volts is needed on the deflection electrodes to produce the same fullscale deflection. The cathode ray tube may then be calibrated with amore convenient andfmor readily obtainable measured Voltage Ec and thescale multiplied by the factor n'.1 By calibrating the beam deflectionusing a' low anode voltage and using a high anode voltage for'mea'surem'entof the pulses, the direct current calibration voltagerequirement may be reduced by a factorof at least ten.

In the drawings:

Fig. 1 is .an illustrationof a parallel wire deflection system foracathode ray tube;

-becomes *excessive.

electrostatic deflection system's Tor use in the cathode ray tube ofFig. -2;

Fig. 5 illustrates an embodiment of a cathode ray "tube oscilloscopeembodying the invention;

Fig. "6 is-a transverse's'ection'al View, taken adj ac'e'nt saiddeflection system, of a cathode ray tube oscilloscope of the typesbheiha'tically illustrated 5 with thedefiletidn coils aiid horizohtalldeflection system omitted for reasons of clarity;

-Fig)? is a fragmentary central longitudinal sec- 'tional view, pa'rtlybroken away, of the oscilloscope shown in Fig. -5, mans the deflectioncoils and horizontal deflection system;

Fig. 8 is a detailed sjec'tich view or aeonnector button assembly of theoscilloscope shown in F rst to 7.

In Fig. *1, a parallel wire 1 deflection system is shown comprising a.pair or *paraum w res 1| and '12 positioned 'fierpehdicula'r to theelectron heath l3 emitted from electron'gun H. 'The'lines of force it ofthe "electrostatic can is shown in Fig. 1a. Thedeflection system may beterminated attih'e end by its characteristic resistance 'IB *ifliberation over a wide band of frequencies is desired. r i,

From Equation 1, the deflection angle of the "electron beamdepends'u'pon the internal-charge per unit Width which canb'e placed onthe system and'upon the potential accelerating the elec tron beamaxially, regardless of the designof the deflection system or the voltageapplied to it. To increaseth'e deflection factor of voltsper'radian'beam'defl ection, it is necessary to decreasethe plateto-pl'atecapacitance for a given value of accelerating voltage. I

The "parallel Wire deflection system, While having a deflection factorless than that of the convei'itional deflection "system using flatflared plates, is not applicable to deflection 'v'oltage's In thecathode ray tube ofFig. 2, a-beamof electrons, shown by referencenumeral [8, is

emitted from electron source 19 of a conven- 'tionalelectron gunandaccelerated by accelerating anode 2B which is connected to ground andto the positive terminal of a battery 21 or other direct current voltagesource. The negative terminal of battery2l is connected toelectronsource IS.

The horizontal deflection system of the cathode Jay-tube is conventionaland isomitted for reasons of clarity and simplicity. -'I} he verticaldeflection system 22 comprises a first deflection electrode or plate 23which is connected to ground in theusual manner and a second deflectionelec- "trode 24 in the form of a circular wire or rod substantiallysurrounded by v a shield 25 containing an aperture 26. Shield 25, likeaccelerating anode 2i], and first deflection electrode 23, is

connected to ground. The ungrounded or "nga tive terminal of a source ofhigh voltage signals,

deflection electrodes 23 and 24i's'indicatd'bythe' plates. the"deflectionsystem at an "angle, as "shown in or radii R1 and "R2.

Ufth'e pulses appears ontne face Z-BO fthB cathode ray tube, as showninjF-i'g92.

The electrostatic defiection system of Fig. 3 includes a pair o'fcoaxia1 cylinders 31 and 32; the leakage field around the slot -34 theouter cylinder 32 is utilized for deflection purposes. The innerc'ylihdr 34 and outer cylinder 32 corresiiondfrespe'ctivelyfto thc'ele'ctro'de anaemia 2t of Fig. -2. The deflection system-6r Fig. 3 alsoincludes a second deflection electrode 3 3 which corresponds to theelectrode 23 '"of Fig. 2. The

kdui pbthtial p'atter n fdi' the configlifation 01 Fig. 3 is SHOW-n by"the "lines 35. 'The relative values or the electric potent als areindicated 'ljy th'e nu'm'erals p'receding "the letter E. The

Width-6f slot 34 chosen has been found to procute too high adeflect'ionfactor for 'rn'any appli'ca'tidns; moreover, considerable variation infield strength 'e'iiists "across the deflection space with a *resultingundesirable *variation of deflec- *tibn"facto'r With defiecticn angle.

An improved electrostatic deflection system '2 2 is shotvh 'in' Fig."4.'Tnebutereyiinder 32 ofFig. "4 has a U -'sh'aped "configuration and theaperture M is considerablyIargerthan'thatof the system of Fig. 3. Thesecond deflection electrode 33' of Fig. 4 is arcuate instead'ofrectan'gular, as in the system or Fig. 3, in order *to more n'earlyap- "proach the deflection-'fleldbtween double flared Since the electronbeam 18' "approaches Fig. 5, and leaves the "deflection system atextreme deflection at "a reverse angl'e, "as shown at iS'f in Fig. 5,the"config'uration of deflection electrode 33 is made to 'coincide "as*c1ose1y" 'as"pos- 'sible 'with the curved ath of the electron beam inorder to obtain the maximum d'efle'ction for a deflection system of fagivenisize and to minimore, "the "curvature 'of "the "eiectrode 33'should be'opposite that o'f tlie equi potential'lines '35 which "areconcave upward. :glance at the values of' potenti'aralongthe'equi-potenti'al lines '35 of Fig. 4 and the deflection'syste'm elements'3! to33' indicate that the deflection fleldis not only-quite uniform inthe 'ccn'tero'f'the deflection area but is greater than tha't'of th'esystem'ci Fig. 3, encompassing five :per cent.'of the total voltageapplied to thetsystem.

The dimensions to beachosen 'for'this deflection system should beassmall as possible for convenience in construction. .JA'lower-limit forthe size will beset by the field intensity at the surface of the innerelectrode 'ofco axial cylinders This A field intensity "is given pk E 11 33 .R1 IHYRI f outer cylinder and E is the'potential' 'difierencebetween cylinders involts.

' "ln' orderto ayoid clild' eniissi'iri,"voltage"gradients should notexceed 10 volts per centimeter.

If a deflecting voltage of 25x10 volts is applied between coaxialcylinders having a diameter relatively low values of voltage, aconsiderable departure from the relative dimensions stated above may bemade without substantially affecting the operation of the deflectionsystem. As the voltages to be measured become higher and higher, thedimensions become increasingly critical.

Referring to Fig. 5, a cathode ray tube oscilloscope, generallyindicated by reference numeral 50, comprises an evacuated glass envelopehaving a neck 52 provided with the usual base 53 and an enlarged portion54 in which the electrostatic deflection system 22' and fluorescentscreen 55 are located. A plurality of pins 56 extending through base 53is electrically connected to the various elements of an electron gun 60mounted at the base end of the tube. The electron gun which may besupported by glass rods 51 rigidly secured within the tube by anysuitable means comprises a cathode 61, a beam-forming electrode 62 andan accelerating anode 63 which are supported in coaxial alignment alongthe cathode ray tube axis by lugs 64 embedded in or otherwise connectedto rods 57. The cathode Bl, beam electrode 62 and anode 63 arepreferably connected to points of increasingly positive potential, inthe usual manner.

Surrounding neck 52 of the tube is a focus coil B5 and deflection coils66 which may comprise a standard television deflection yoke. One set ofdeflection coils furnishes the horizontal time base deflection of theoscilloscope trace while the other set of coils provides a verticaldeflection of the electron beam.

Although the use of a magnetic horizontal deflection system is moreconvenient, an electrostatic horizontal deflection system may be used inlieu thereof.

The vertical electrostatic deflection system 22' is the one shown inFig. 4 comprising a first electrode 33, a. second electrode 3! and anapertured shield 32' surrounding electrode 31'. The electron beam isdeflected from its original path coincident with the cathode ray tubeaxis as shown by dotted line l8 so that, in the absence of anydeflection signal to the electrostatic deflection system 22', theelectron beam strikes the top of the screen at a point A. Theelectrostatic defiection system, therefore, is displaced from the tubeaxis so that the electron beam can pass through the field between theelectrodes 32' and 33'. At maximum deflection, corresponding to themaximum input signal to deflection electrodes 3i and 33', the electronbeam is bent downward as shown by dotted line I8" and strikes the bottomof the screen at a point B. By displacing the electrostatic deflectionsystem 22' from the tube axis the entire face of the cathode ray tubescreen may be utilized instead of just half of the screen wheneverpulses of only one polarity are to be measured.

The physical arrangement of the electrostatic deflection system 22'within the enlarged portion 54 of envelope 5| is shown in Figs. 6 to 8in which the elements corresponding to those of Fig.5 are shown by likereference numerals. An

electrical connection to shield 32' as well as a mechanical support forsaid shield will now be described. The deflection shield 32 is suspendedfrom the wall of the tube by means of a connector button H sealed in theglass envelope 5! having a loop portion 12 through which a looped rod orwire 13 is positioned. Wire 13 is mechanically connected to two wireloops which encircle wire 13 and are spot welded to the top surface ofshield 32. Connector button ll and elements 12 to 15 also provide asuitable electrical connection from the external deflection voltagesource to the shield.

The deflection electrode 33' is spaced from shield 32' by two sets ofwire loops l5 welded to wires 16; the latter are, in turn, welded orotherwise secured to electrode 33'. An electrical connection fromelectrode 33' externally of the tube envelope 5! is provided by means ofthe assembly shown in detail in Fig. 8. A wire loop is attached to thebottom of electrode 33' and engages a wire loop 8! welded to the insidewall of connector tube 82 at one end thereof. A connector button 83 isconnected to the other end of connector tube 82 by means of a secondwire loop 84 welded to the connector button and soldered within tube 82by a solder ring 85, as shown clearly in Fig. 8. Electrode 33' andshield 32', as well as the supporting wires and contact buttons, arepreferably made of a polished material, such as stainless steel. It isalso possible to connect shield 32' and reflection electrode 33'internally to the acceleratingv anode 63 (see Fig. 5), in which case noexternal connections to connector buttons ll and 83 need be used.

The deflection electrode 3| consists of a rod preferably made ofstainless steel polished to a mirror finish to minimize cold emissionresulting from irregularities in the surface of the rod. Electrode 3| isadapted to be inserted within a tubular recess in one end of each of thetwo metal rods 99, 9B which extends through the ends of the elongatedtransverse portion 9! of tube envelope 5|. A glass disk 93 surroundingeach of rods provides a means for forming a hermetic seal between therod and the glass envelope. The end of rods 98 into which electrode 3iis inserted is slotted so as to hold the rodshaped electrode firmly inposition within the tube.

This invention is not limited to the particular details of construction,materials and processes described, as many equivalents will suggestthemselves to those skilled in the art. It is accordingly desired thatthe appended claims be given a broad interpretation commensurate withthe scope of the invention within the art.

, What is claimed is:

1. A cathode ray tube for measurement of high voltage signals comprisingan envelope containing a means for producing a concentrated electronbeam, a first set of deflecting electrodes for producing a deflection ofsaid beam in a first di rection, a second set of deflection electrodesfor producing deflection of said beam in a direction normal to saidflrst direction, said second set of electrodes including a firstunshielded electrode, and a second electrode arranged normal to saidbeam and surrounded by an apertured shield, means for connecting saidfirst electrode and said shield to one terminal of a source of said highvoltage signals and means for connecting said second electrode to theother terminal of said source.

2 A cathode ray tube for measurement of high voltage signals comprisingan envelope containa fer reemies a eq cen rate ele tron beam, anelectrostatic defile ion system tor producing. a deflecti n of sai bee.a deflection system including a first unshielded electrode, and a secondelectrode. surrounded by. an apertured shield, means. for connectingsaid first electrode and said shield to one terminal of a source of saidhigh voltage signals and means for connecting said second electrode tothe other terminal of said source.

3. A cathode ray tube for the measurement of high voltage pulsescomprising an electron gun positioned at one end of said tube forproducing an electron beam, a focusing electrode and an acceleratinganode, a screen disposed at the other end of said tube and adapted to beilluminated over the portion impinged by said electron beam, and anelectrostatic deflection system to which said pulses are directlyapplied interposed between said accelerating electrode and said screenfor deflecting said electron beam from its original path, saiddeflection system comprising a first unshielded electrode and a secondelectrode surrounded by a shield, said shield having an aperture thereinarranged to partially expose said first and second electrode to oneanother.

4. A cathode ray tube comprising an envelope, means including a cathodeand an accelerating anode for producing a concentrated electron beamtherein, a fluorescent screen adapted to be impinged by said electronbeam for providing a visual presentation of the position of said beam, abias deflection system interposed between said electron gun and saidscreen for producing a fixed deflection of said beam away from thelongitudinal axis of said tube and a second deflection system locatedbetween said first deflection system and said screen and displaced fromsaid longitudinal axis, said second deflection system comprising a firstunshielded electrode and a second electrode disposed transverse to saidelectron beam, said second electrode being surrounded by a shield havingan aperture arranged to partially expose said first and secondelectrodes to one another.

5. A cathode ray tube comprising an envelope, means including a cathodeand an accelerating anode for producing a concentrated electron beamtherein, a fluorescent screen adapted to be impinged by said electronbeam for providing a visual presentation of the position of said beam, ahorizontal deflection system and a first vertical deflection systeminterposed between said electron gun and said screen, said firstdeflection system being adapted to produce a fixed deflection of saidbeam away from the longitudinal axis of said tube and a second verticaldeflection system to which signals to be measured are applied, saidsecond vertical deflection system being located between said firstdeflection system and said screen and displaced from said longitudinalaxis, said second vertical deflection system comprising a firstunshielded electrode and a second electrode disposed transverse to saidelectron beam, said second electrode being surrounded by a shield havingan aperture arranged to partially expose said first and secondelectrodes to one another.

6. A cathode ray tube for measurement of high voltage input signals of agiven polarity comprising an envelope containing at one end thereof anelectron gun for producing a concentrated electron beam and afluorescent screen at said other end, bias deflection meansv fordeflecting said beam from the. central longitudinal axis of: said tubein the. absence. of said signals, an electro: static deflection systeminterposed. between said bias deflection means and said screen andincluding an unshielded electrode. and an electrode. partially enclosedby.- a shield having an aperture. therein arranged to partially exposesaid first and said second electrodes to one another, said de-s.flection system being displaced from said axis so that substantially theentire. portion of said screen may. be'utilized for presentation ofsaidinput signals.

7. A cathode. ray tubefor. measurement of high voltage input signals ofa given polarity comprising an envelope containing at one end thereof anelectron gun for producing a concentrated electron beam and afluorescent screen at said other end, bias deflection means fordeflecting said beam from the central longitudinal axis of said tube inthe absence of said signals, an electrostatic deflection systeminterposed between said bias deflection means and said screen andincluding an unshielded electrode and an electrode partially enclosed bya shield having an aperture therein arranged to partially expose saidfirst and said second electrodes to one another, said deflection systembeing displaced from said axis so that substantially the entire portionof said screen may be utilized for presentation of said input signals,means for connecting said first electrode and said shield to oneterminal of a source of said high voltage signals and means forconnecting said second electrode to the other terminal of said source.

8. A cathode ray tube for measurement of high voltage signals comprisingan envelope containing a means for producing a concentrated electronbeam, a first set of deflection electrodes for producing a deflection ofsaid beam in a first direction, a second set of deflection electrodesfor producing deflection of said beam in a direction normal to saidfirst direction, said second set of electrodes including a firstelectrode having an arcuate configuration transverse to said beam, and asecond electrode, said first and second electrodes having theirlongitudinal axes arranged normal to said electron beam and spaced fromsaid first electrode, and an apertured shield surrounding said secondelectrode, said aperture having a length greater than its width andbeing arranged to partially expose said first and said second electrodesto one another.

9. A cathode ray tube for measurement of high voltage signals comprisingan envelope containing a means for producing a concentrated electronbeam, a first set of deflection electrodes for producing a deflection ofsaid beam in a first direction, a second set of deflection electrodesfor producing deflection of said beam in a direction normal to saidfirst direction, said second set of electrodes including a firstelectrode having an arcuate configuration transverse to said beam,

and a second electrode circular in cross section whose longitudinal axisis arranged normal to said electron beam and spaced from said firstelectrode, and a curved apertured shield surrounding said secondelectrode, said aperture being arahged to partially expose said firstand said second electrodes to one another, the radius of curvature ofsaid shield being approximately six times the radius of said secondelectrode.

10. An electrostatic deflection system for deflection of an electronbeam comprising a first deflection electrode having an arcuateconfiguration transverse to said beam, and a second deflection electrodespaced from said first electrode, said first and second electrodeshaving their longitudinal axes arranged normal to said electron beam,and a curved apertured shield surrounding said second electrode, saidaperture having a length greater than its Width and being arranged topartially expose said first and said second electrodes to one another.

11. An electrostatic deflection system as recited in claim 10 whereinthe radius of curvature of said shield is approximately six times theradius of said second electrode.

RUDOLF C. HERGENROTHER. HERMANN GUNTHER RUDENBERG.

12 REFERENCES CITED UNITED STATES PATENTS Number Name Date Wilson Aug.9, i938 Sprague et al. June 6, 1939 Wideroe Apr. 24, 1951

